Summary implemented on PCS uses outgoing requests to various APIs to collect all the information needed to combine and process in order to generate the summary for a given wiki page.
More specifically:

• MW action API
  • Page metadata
  • Revision information
  • Page props
  • ...
• MW REST API
  • Parsoid
• Wikidata
  • Page description

We need to map these dependencies to MW resources.
That means either direct access to DB or wiring via extensions services.